Mixing valves are, in general, well known and a typical such valve comprises a through channel which is connected in series with a hot water supply line. A cold water inlet is also provided in the mixing valve and it communicates with the through channel at the upstream side of a thermostat element. The thermostat element is located in the channel and it functions to control the temperature of water passing from the mixing valve. A regulator valve element is located in a fluid passage between the cold water inlet and the through channel, and such valve element is controlled by the thermostat element to regulate the quantity of cold water which is admitted into the through channel to mix with the hot water. Thus, the thermostat element senses the temperature of the hot-and-cold water mix and controls the regulator valve element to provide a mix ratio that results in a required (pre-determined) outflow temperature. The thermostat element is selected or adjustable to provide for the required outflow temperature.
A number of different types of mixing valves which embody the above described construction are known and they incorporate mechanisms of varying degrees of complexity. However, it is believed that all prior art mixing valves are incapable of fail-safe operation, in the sense that they do not function to provide a low temperature outflow in the event that the thermostat element should fail to operate. For example, in the known mixing valves which use a wax-filled thermostat element, the regulating valve element will not be actuated and, in a worst case situation, no cold water will be admitted into the hot water stream if the thermostat element fails to function as a result of wax bleeding away from such element. The temperature of the outflowing water will then be approximately equal to that of the inflowing water, with potentially hazardous results.